486 SECTIONAL TRANSACTIONS.—K. 
they can be observed actually in progress, either habitually or occasionally, under 
specially favourable circumstances. 
As a result we are able to account for certain of these apparent morphological 
anomalies and to discard others as fictions, as e.g., the commissural stigma. 
3. Prof. H. H. Drxon, F.R.S., and Mr. Nicen G. Bauu.—The 
Extraction of Sap from Living Leaves by means of Compressed 
Air. 
Branches of Vilia americana and Sambucus nigra were enclosed in a strong 
cylinder in such a way that their cut ends protruded. Compressed air at 
pressures up to 20 atmospheres was admitted into the cylinder, and the liquid 
which exuded from the cut end of the branch was collected. This liquid was 
found to be completely, or almost completely, free from sugars. Experiments 
carried out in early and late summer gave similar results. After the leaf-cells 
had been made permeable by means of toluene vapour the sugar in the expressed 
sap amounted to about 5 per cent. 
4. Prof. W. Nreitson Jones.—Regeneration of Roots and Shoots in 
Cuttings of Seakale. 
Experiments on the regeneration of roots and shoots in root-cuttings of 
seakale point to the following conclusions :— 
(1) The end of the cutting nearest the original root apex shows a marked 
capacity for producing roots. There is only a slight tendency for this capacity 
to extend any distance from this end, and none of the methods tried has been 
successful in appreciably lengthening this distance. 
(2) The end of the cutting nearest the original stem apex shows a marked 
capacity for shoot production. There is a strong tendency for this capacity to 
spread along the cutting. Various means accentuate this tendency. 
(3) Short pieces of root when they regenerate always produce shoots from 
both ends. Any roots that are produced arise from one end only. 
(4) Repeated attempts have been made to correlate this ‘regeneration 
gradient ’ with a gradient of electrical potential or hydrogen-ion concentration, 
but without conclusive results. 
5. Dr. M. C. Rayvner.—Contributions to the Biology of Mycorrhiza 
im the Ericacee. 
(1) ‘ Digestion ’ stages in roots. 
The root mycorrhiza of Calluna vulgaris exhibits digestion stages resembling 
those found in the root-cells of orchids. It is believed that the relations between 
root-cells and fungus show seasonal periodicity, the digestion of mycelium 
reaching a maximum during the autumn months. 
(2) Formation of mycorrhiza in ‘ cuttings’ of Calluna. 
The roots of shoot cuttings, struck under controlled conditions in sterilised 
sand, show infection of the same type as that exhibited by other young roots. 
The observations recorded by Christoph have not been confirmed. 
6. Dr. F. G. Grecory.—The Interrelation of Light and Temperature 
in Growth and Assimilation. 
(1) Growth of leaf-area and increase of dry weight in the greenhouse. The 
method of studying growth in leaf-area and the errors of the method. Growth 
of leaf-area during summer and winter. The compound-interest law of leaf- 
growth and its modifications when light intensity is comparatively low. 
(2) Growth under continuous illumination at different constant temperatures. 
The effect_of temperature on the growth of single leaves and of the total leaf- 
surface. The effect on the net assimilation rate. Total assimilation is dependent 
primarily on leaf-surface growth. Growth at supra-optimal temperatures. The 
law of the optimum and the law of limiting factors. Growth and assimilation 
conditioned by light intensity and temperature under all conditions. 
(3) The energy-etficiency of plants. Variation of efficiency with temperature. 
The hypothesis of shifting optima and the law of limiting factors. 
